1. Field of the Invention
The present invention relates to a sump standpipe for use in a hydraulic system and in particular to a sump standpipe having a side inlet port as well as a top inlet port to eliminate the formation of a vortex above the standpipe and achieve a stable oil level control.
2. Description of Related Art
When a tractor transmission shares oil with the rest of the vehicle hydraulic system, such as an axle lubricating system and a hydraulic steering system, the transmission sump oil has to be circulated or mixed with the oil in the rest of the hydraulic system. The oil level in the transmission sump has to be constantly maintained at an optimized level to reduce windage power loss from high-speed gears turning in the oil and to meet the transmission pump suction requirements.
The conventional approach to maintaining the oil level in the sump is to install a standpipe in the transmission sump that connects to a transfer pump inlet. Since the transfer pump typically has a greater flow rate than the incoming oil flow to the transmission, the oil level in the transmission sump is pulled down to the approximate height of the standpipe as shown in FIG. 3. Due to downward suction around the standpipe inlet, a vortex will form in the oil above the standpipe. As soon as a vortex around the standpipe is formed, a large amount of air will be drawn into the transfer pump. This can reduce the oil flow out of the sump to an amount less than the incoming oil flow, causing the oil level in the sump to increase. The oil level will keep increasing until the vortex becomes too deep to maintain, after which the transfer pump will draw in only oil, without any air.
The depth of the vortex will depend on the flow velocity through the standpipe, the amount of air mixed with the oil and the oil viscosity. In a vehicle application, the transfer pump speed can vary greatly during operation due to engine speed variation. Operating temperatures can also vary from xe2x88x9232 to 100xc2x0 C. At conditions of high oil flow (velocity) and cold oil temperature (high oil viscosity), the depth of the vortex can be as much as 150 mm. The creation of a vortex and its subsequent termination as the oil level increases will cause the flow of oil to the transfer pump to fluctuate between almost all air to all oil. This will cause downstream pressure surges and flow interruptions.
In most cases, the transmission output gear is slightly dipped in sump oil so that the gear teeth can pick up a small amount of oil to lube the gear and provide splash lubrication to other components in the transmission. Increasing the oil level in the sump can cause the output gear to be submerged in the oil. This causes sump oil foaming during high speeds associated with vehicle transport operations that increase windage loss. If the extra flow capacity of the transfer pump cannot make up the drop in efficiency caused by foamy oil, the transmission begins to overfill, leading to an imbalance in the oil level in different components in the hydraulic system.
To prevent the formation of a vortex, the standpipe of the present invention has ports on the side of the standpipe and one smaller port on the top of the standpipe. The majority of the oil flow is distributed to the two side ports and subsequently, the downward suction flow velocity is reduced. This eliminates a vortex above the standpipe inlet. Since air flows easier through an orifice than does oil, the top port can be sized small enough to reduce the downward oil velocity without restricting the exit of airflow upward through the standpipe.
The new standpipe reduces or eliminates the oil level fluctuation due to engine speed and/or operating temperature changes that would previously have created a vortex. In addition, the standpipe reduces the extent of oil aeration in the transmission system by maintaining oil level at or near the optimum design level under all operating conditions. Controlling the sump oil level at the optimum level will reduce the windage loss and improve transmission pump suction conditions. In hydraulic systems where the fluid output of the transfer pump is utilized for productive uses such as lubrication of other components or cooling, the standpipe of the present invention provides more overall consistency in the oil flow.